1. Field of the Invention
This invention relates to lenses for use in photographic printers.
2. Description Relative to the Prior Art
The processing and printing of photographic roll film includes an early step of splicing a plurality of similar film strips end-to-end. The spliced strips should be similar in size (e.g. 35 mm or 110 or 126) although not necessarily in length. Also, they should be similar in requiring the same developing process. Most of the characteristics, e.g., size and type are detectable prior to the strips being spliced end-to-end. One characteristic is not detectable unless the photographer has given appropriate information to the processing laboratory. This characteristic is size of frame of the latent images on the film. For example, with reference to FIGS. 6 & 7 of the accompanying drawings, the latent images on a 35 mm film might be full-frame images 30, i.e., 24 mm by 36 mm with the longer dimension parallel to the length of the strip 31, or they might be half-frame images 32, i.e. 24 mm.times.18 mm with the shorter dimension parallel to the length of the strip 33.
After the supposedly similar film strips 31, 33 have been spliced end-to-end, they are reeled up. The reel is placed at the beginning of a continuous processing apparatus in which the latent images are developed and fixed. The dried film is reeled up at the end of the apparatus and is transferred to a printer.
The continuous strip of film is led off its reel through the printer and prints are made at a rate of many thousands per hour. The direction of feed of the film strip through the printer is parallel to the direction of feed of a continuous web of sensitized paper through the printer. Thus, with full-frame 35 mm negatives with the lesser dimension of the negative image transverse to the film, the lesser dimension of the image 34 created on the web 35 of paper is transverse to the paper web. Thus, the width of the web 34 of paper is chosen to be equal to the desired lesser dimension of the finished print, see accompanying FIG. 8.
A problem arises when a strip of film which has half-frame images 32 is spliced in with film strips which have full-frame images 30. If no alternative provision was made, two images 36 and 36' would be printed on the paper web 35 from two adjacent half-frame images 32, as illustrated in FIG. 9. Each image 36 and 36' would be about half the size of the images 34 from full-frame negatives, i.e. about half the size the customer wants.
Endeavors to overcome the problem caused by the occasional presence of films with half-frame images have included a visual inspection of the spliced film strips after processing. When a strip with half-frame images is detected it is cut out of the continuous strip. The rejoined, continuous strip can then be printed without problem. The extracted film strips carrying half-frame images are then printed individually under human control. Such procedures are evidently time-consuming and costly.
German Offenlegungschrift 32 48 807 has proposed that a printer be provided with two interchangeable lenses one of which rotates the image through 90.degree.. If the non-image-rotating lens is used to print full-frame images and the image-rotating lens is used to print half-frame images, the longer dimension of the images derived from both sizes of negative frame, can be oriented parallel to the length of the paper web. The image sizes can be made the same by appropriate selection of magnification of each lens. DE-A No. 32 48 807 describes an image-rotating lens which includes a plurality of elements with an air space in the middle which is located a dove prism. A known characteristic of a dove prism, used appropriately, is that it rotates an image by twice its own rotation. DE-A No. 32 48 807 recognizes a problem created by the use of the dove prism and it is related to the fact that the dove prism contains a single reflecting surface. The dove prism causes a reversion of the image produced by the lens including the dove prism when compared to the image produced by the lens without the dove prism (i.e., the full-frame lens). DE-A No. 32 48 807 states that this problem could be overcome by turning the film over when printing with the lens including the dove prism. This procedure would overcome the reversion problem but would obviously be inconvenient. Also, it would means that when the film is so turned over, the light would be directed first through the emulsion and then through the transparent film base, which is known to be undesirable. DE-A No. 32 48 807 discloses that in order to avoid the undesirable necessity to turn the film over when printing half-frame images with the lens including the dove prism, the other lens (for full-frame images) should also include a dove prism. This other dove prism, would be so oriented as to cause no rotation of the image but it would inherently produce reversion. Thus, both the lenses would cause reversion and one would rotate. This overcomes the necessity to turn the film over, but it requires that all portions of the film strip passed through the printer be in a `turned over` condition, i.e, that the emulsion be on the side of the film base nearer the light source. Thus, the arrangement preferred in DE-A No. 32 48 807 has the disadvantage of operating in an undesirable manner. This problem may be restated as being that whereas a conventional printer lens causes inversion of the image, which allows the emulsion to be on the side of the base towards the paper, the preferred printer of DE A No. 32 48 807, with each of its two lenses including a dove prism, causes inversion and inversion and therefore requires that the emulsion be on the side of the base away from the paper.